WASHINGTON -- After months of trading insults and threats of nuclear annihilation, U.S. President Donald Trump agreed to meet with North Korean leader Kim Jung Un by the end of May to negotiate an end to Pyongyang's nuclear weapons program, South Korean and U.S. officials said Thursday. No sitting American president has ever met with a North Korea leader.

The meeting would be unprecedented during seven decades of animosity between the U.S. and North Korea. The countries remain in a state of war because the 1950-53 Korean War ended with an armistice and not a peace treaty.

"Great progress being made," after the South Korean national security director, Chung Eui-yong, announced the plans to reporters in a hastily called appearance on a White House driveway.

Trump added that sanctions will remain in place until there's a deal.

Trump took office vowing to stop North Korea from attaining a nuclear-tipped missile that could reach the U.S. mainland, a goal that Pyongyang is on the cusp of reaching. He's oscillated between threats and insults directed at Kim that have fueled fears of war, and more conciliatory rhetoric.

The historic announcement comes during a period of unparalleled tumult in the West Wing, with the president's policy agenda stalled and morale sinking as staff departures proliferate and disrupt efforts to instil more discipline and order.

Trump clearly relished the news of the planned summit. He had made a surprise visit to the White House press briefing room on Thursday afternoon to alert reporters of a "major statement" on North Korea by South Korea. When asked by an ABC reporter if it was about talks with North Korea, he replied: "It's almost beyond that. Hopefully, you will give me credit."

Earlier Thursday, Chung had briefed Trump and other top U.S. officials about a rare meeting with Kim in the North Korean capital. During that meeting, the rival Koreas agreed to hold a leadership summit in late April, the first in a decade.

Kim "expressed his eagerness to meet President Trump as soon as possible," Chung told reporters. "President Trump appreciated the briefing and said he would meet Kim Jong Un by May to achieve permanent denuclearization."

The White House said Trump's meeting with Kim would take place "at a place and time to be determined."

"Kim Jong Un talked about denuclearization with the South Korean Representatives, not just a freeze," Trump said in a tweet. "Also, no missile testing by North Korea during this period of time."

It marks a dramatic shift in Trump's stance toward North Korea. He has threatened the pariah nation with "fire and fury" if its threats against the U.S. and its allies continued. He has derided Kim by referring to him as "Little Rocket Man." Kim has pilloried Trump as "senile" and a "dotard."

After Kim repeated threats against the U.S. in a New Year's address and mentioned the "nuclear button" on his office desk, Trump responded by tweeting that he has a nuclear button, too, "but it is a much bigger & more powerful one than his, and my Button works!"

North Korea appeared to confirm the summit plans. A senior North Korean diplomat at the United Nations in New York, Pak Song Il, told The Washington Post in an email that the invitation was the result of Kim's "broad minded and resolute decision" to contribute to the peace and security of the Korean Peninsula.

By the "great courageous decision of our Supreme Leader, we can take the new aspect to secure the peace and stability in the Korean Peninsula and the East Asia region," Pak wrote.

On Tuesday after leaving Pyongyang, Chung had publicized that North Korea was offering talks with the United States on denuclearization and normalizing ties. But the proposal for a summit still came as a surprise, and will raise questions about whether the two sides are ready for such a high-level meeting.

Just a few hours earlier, U.S. Secretary of State Rex Tillerson, who is travelling in Africa, had said the adversaries were still a long way from holding negotiations.

Chung, who credited Trump's "maximum pressure" campaign for the diplomatic opening on the nuclear issue, said Kim understands that routine U.S.-South Korea military drills "must continue."

The drills were suspended during the Winter Olympics recently hosted by South Korea, which provided impetus for the inter-Korea rapprochement. The drills are expected to resume next month and had widely been seen as an obstacle to talks. North Korea has long protested the military manoeuvrs south of the divided Korean Peninsula as a rehearsal for invading the North.

When the South Korean delegation briefed Trump in the Oval Office, he was joined by a number of top advisers, including Defence Secretary Jim Mattis, National Security Adviser H.R. McMaster, chief of staff John Kelly and the director of national intelligence, among others, according to a senior Trump administration official who briefed reporters after the announcement. The official, who was not authorized to discuss the sensitive diplomatic issue by name and spoke on condition of anonymity, said there was no letter from Kim to Trump, just an oral briefing from the South Korean officials.

The planned summit was welcomed by arms control advocates, but got varying responses from Republican lawmakers.

House Foreign Affairs Committee chairman Ed Royce said the invitation was a sign that sanction pressure was working but he was skeptical of North Korea's motives. Sen. Lindsey Graham warned Kim that "the worst possible thing you can do is meet with President Trump in person and try to play him. If you do that, it will be the end of you -- and your regime."

Darryl Kimball, executive director of the Arms Control Association, said it was too much to expect a single Trump-Kim summit could immediately resolve the nuclear issue that has bedeviled U.S. administrations since the early 1990s, when the North first began producing fissile material for bombs.

"But if the U.S. works closely and intensively with our South Korean allies in its approach to North Korea, a summit offers the potential for starting a serious process that could move us decisively away from the current crisis," Kimball said.

Associated Press writers Jill Colvin, Zeke Miller, Catherine Lucey, Ken Thomas and Darlene Superville contributed to this report.